In recent years, attention has been focused on a hybrid vehicle that uses both of an engine and a motor for travel of the vehicle to achieve higher fuel efficiency. In relation to control of an engine rotation speed of such a hybrid vehicle, Japanese Patent Laying-Open No. 2001-304022 discloses a device for controlling a rotation speed of an internal combustion engine, in which device, when idle control of the internal combustion engine and rotation speed control that controls a rotation speed of the internal combustion engine by a request for control other than the idle control are performed, reliability of the idle control is improved.
In Japanese Patent Laying-Open No. 2001-304022 described above, there is performed a gradually-changing process in which an engine target rotation speed is gradually changed to lower the same. Therefore, excessive driving of a valve for closing the valve is avoided.
However, the hybrid vehicle can assume various control states, and hence performing the same gradually-changing process all the time may not be suitable depending on a control state of the vehicle, and may cause vibrations perceived by a passenger.